Background of the Invention Current moulds for the continuous casting of round blooms are usually constructed of tubular body, its diameter in its upper part is slightly linearly decreasing from the input of hot metal towards its middle. This taper in the upper part of the mould body varies from 1 W to 2 % and it is important regarding gradual shrink of the casting as a result of its running solidification in the mould and the need of additional providing of offtake and transfer of heat from the casting to the mould body and need of constant conveyance during its move through the mould.

There are also known so called parabolic moulds with better heat transfer and casting conveyance, because their parabolic cross section renders better the process of shrink of cast material.

The problem of the moulds with bigger taper is the fact that at actual internal dimensions they enable trouble-free continuous casting of steel in given range of chemical composition, mainly concerning the contents of carbon. For example, at higher taper of the mould the jam of casting in the mould can occur for steel with higher carbon content, e. g. 1 t of weight. On the contrary, with the smaller taper and

casting the steel with lower content of carbon, such as 0, 1 0 of weight, the air gaps between created cortex of the casting-and wall of the mould can occur as the result of bigger shrink of the casting with negative impacts to heat transfer, conveyance of the casting in the mould and the final quality of the casting.

Summary of the Invention Above stated disadvantages are substantially eliminated by the round mould for the steel continuous casting, comprising of the mould body, which principle consists in the fact that the upper part of the mould body at the input of liquid steel at its internal surface is equipped with continuously diminishing corrugation towards its middle part.

The corrugation of the mould body is favorably done in its upper part in the lenght (1) in the range of 30 to 50 0 of the total lenght (L) of the mould body from its upper part. The corrugation is also favorably created by the circle advancing in the sinusoid curve.

The principle of the invention then consists in the fact that the maximum amplitude of the sinusoid curve of the corrugation is at the top edge of the mould whilst the maximum amplitude is 0, 40 % to 0, 55 % of the diameter (D) of the mould body. With advantageous design of the invention, the sinusoid curve touches the external side of the original circle of the edge of inlet aperture of the mould body in 15 to 25 touch spots.

The corrugation of the internal surface of the upper part of the mould is accomplished by shape scoop where the excess of metal is occurring, this ensures constant contact of the casting with the mould wall and thus the heat transfer and stable conveyance of the casting through the mould. The corrugation passes back to the round cross section in the middle part of the mould whilst the bottom part of the mould is the same as for current moulds. The maximum depth of the scoop correspondent to the corrugation created by the sinusoid curve and the size of its amplitude is dependant on the diameter of the mould, for example the mould with the diameter of 410 mm has optimum scoop by the top edge ca. 2 mm. Regarding the fact, that the depth of scoop is continuously decreasing towards the middle of the mould, the peaks of scoop reach also higher taper, e. g. by 5 % more than for the points of contact, where the corrugation curve touches the original circle and where the scoop is zero and the taper there is ca. 1, 4 W. Whilst the number of points of contact is not depending on the diameter of the mould, the depth of scoop is linearly increasing with the bigger diameter or decreasing with the smaller diameter.

Besides improved conveyance of the bloom and better transfer of heat, the advantage of the mould according to the invention is also achievement of more balanced growth of the crust and decreasing of depressions at the surface of the bloom, this decreases the occurrence of leaks and longitudinal cracks, mainly for steels with the carbon contents less than 0, 2 0 of weight, and enables to cast the steels in the broad range of carbon contents, e. g. from 0, 06 % to 1, 00 %.

Brief Description of the Drawings The invention will be clarified by the figures of particular example of round mould according to the invention, FIG. 1 draws out the scheme of spatial view and FIG. 2 shows the section of the top edge at the inlet aperture.

Description of the prefered embodiment The round mould for the continuous casting machine depicted on FIG. 1 and FIG. 2 is composed of cylindrical body 1 with the upper part 2, which is equipped at the inlet of liquid steel at its internal surface by the continuously to zero decreasing corrugation 4 towards its medium part 3. The corrugation 4 of the mould body 1 is carried out in the upper part 2 with the lenght (1) amounting to 40 0 of the total lenght (L) of the mould body 1 from its top edge 5. The bottom part of the mould body 1 is circular. The corrugation 4 is created by the sinusoid curve 6 with the amplitude (x) at the top edge 5 of the mould body 1, whilst the amplitude (x) is 0, 48 0 of the diameter (D) of the mould body 1. The wavelenght of the sunusoid curve 6 is selected in the manner that it touches the original circle 7 of the edge 5 of the mould body 1 in 20 points of contact 8.

Corrugation 4 then creates pockets 9 for creation of excessive liquid metal.

Field of the Application The invention can be. utilized at all moulds at the continuous casting machines of vertical type.